Reproducing method for magneto-optic recording medium, and magneto-optic disk device

ABSTRACT

A reproducing apparatus reproduces a signal recorded in a magneto-optical disk. The magneto-optical disk includes a layered structure having a recording layer, an intermediate layer and a reproducing layer. Laser light is illuminated from an optical head to the magneto-optical disk in such an intensity that no magnetic domain is transferred from the recording layer to the reproducing layer only by the laser light. In this state, alternating magnetic field is applied through a magnetic head to the magneto-optical disk, thereby concurrently causing transfer and expansion of a magnetic domain to the reproducing layer. As a result, transfer of the magnetic domain is effected with expansion.

TECHNICAL FIELD

This invention relates to a reproducing method with a magneto-opticalrecording medium and, more particularly to a reproducing method with amagneto-optical recording medium including, for example, recording andreproducing layers so that the microscopic domain can be recorded intothe recording layer during recording and the recorded magnetic domain ofthe recording layer be expanded and transferred into the reproducinglayer during reproduction.

Furthermore, the invention is concerned with a reproducing method andmagneto-optical disk apparatus which reproduces a signal by optimallysetting a laser light power level during expanding and reproducing themagnetic domain, wherein the magneto-optical disk apparatus performssignal recording and/or reproducing by using laser light and magneticfield applied to the magneto-optical recording medium.

Prior Art

Attentions have being drawn to magneto-optical recording mediums asrewritable recording mediums that are high in memory capacity andreliability. They have being put into practical use as computermemories, etc. Meanwhile, standardization has being put forward formagneto-optical recording mediums having a recording capacity of 6.0 Gbytes toward a standard of AS-MO (Advanced Storage Magneto-Opticaldisk). It has been a practice to reproduce a signal from a high-densitymagneto-optical recording medium as mentioned above by an MSR(Magnetically Induced Super Resolution) method that irradiates laserlight form a detection window in the reproducing layer of themagneto-optical recording medium so that a magnetic domain istransferred from the recording layer into the formed detection window,thereby carrying out signal reproduction.

Meanwhile, a technology of expanding and reproducing a magnetic domainhas been developed, wherein alternating magnetic field is applied duringreproducing signals from a magneto-optical recording medium so that themagnetic domain present in the recording layer can be expanded andtransferred to the reproducing layer by the applications of laser lightand alternating magnetic field, thus reproducing signals. There has beenan proposal on a magneto-optical recording medium utilizing thistechnology to record and/or reproduce a signal of 14-G bytes.

The recording/reproducing apparatuses for a magneto-optical recordingmedium of this kind have been disclosed, for example, in JapaneseLaid-open No. H6-295479 (Oct. 21, 1994) [G11B 11/10], Japanese Laid-openNo. H8-7350 (Jan. 12, 1996) [G11B 11/10] and so on.

The magneto-optical recording medium 10, as shown in FIG. 1, includes arecording layer 14 and reproducing layer 16 formed by respectivemagnetic layers on a substrate 12. An intermediate layer 18 is formedbetween the recording layer 14 and the reproducing layer 16 while aprotection layer 20 is formed on the recording layer 14. Incidentally,although the intermediate layer 18 herein is formed by a non-magneticlayer, it may be made by a magnetic layer. Also, the recording layer 14and reproducing layer 16 can be formed of arbitrary known magneticmaterials.

Referring to FIG. 2, microscopic record magnetic domains are recordedwithin the recording layer 14 of the magneto-optical recording medium 10through the use of a magnetic head (not shown). During reproduction, therecord magnetic domain 22 of the recording layer 14 is transferred intothe reproducing layer 16 by illuminating laser light 24, as shown inFIG. 3.

Specifically, laser light 24 provides a temperature profile to themagneto-optical recording medium 10 as shown in FIG. 3. The temperatureis highest at around a spot center but gradually decreased toward anoutward thereof. It should be noted that, where the magneto-opticalrecording medium is for example a disk, the temperature profile isdifferent in slant between forward and backward with respect to a movingdirection of the magneto-optical recording medium. The temperaturegradient is steeply slanted in a region of the disk entering into thelaser spot as compared to that of a region exiting therefrom. Byutilizing such a temperature profile, the magneto-optical recordingmedium 10 is increased in temperature up to a desired point.

Referring back to FIG. 2(A), if laser light 24 is illuminated onto themagneto-optical recording medium 10, the magneto-optical recordingmedium 10 is raised in temperature in accordance with the temperatureprofile as shown in FIG. 3. The reproducing layer 16 herein is formed bya magnetic layer that, at from room temperature to the Curie temperatureTc, is enriched in transition metal and assumes a perpendicular magneticanisotropy film. Consequently, if laser light 24 is illuminated, thereproducing layer 16 is increased in temperature, being decreased incoercivity. Due to this, the record magnetic domain 22 within therecording layer 14 is transferred into the reproducing layer 16 throughthe intermediate layer 18 due to static magnetic coupling. Thus, atransferred magnetic domain 26 is formed within the reproducing layer16. The transferred magnetic domain 26 is formed in a positioncorresponding to the record magnetic domain 22.

After forming a transferred magnetic domain 26 in the reproducing layer16, an external magnetic field Hex as shown in FIG. 2(B) is appliedthrough a not-shown magnetic head. This external magnetic field Hex isof an alternating magnetic field. This alternating magnetic field isapplied for at lease 1 period, preferably 2-4 periods while one magneticdomain is passing through a hot spot 24 a formed due to the laser light24. The alternating magnetic field, or external magnetic field, ifapplied in the same direction (same polarity) as that of the transferredmagnetic domain 26, causes the transferred magnetic domain 26 to expandin its diameter, thus forming expanded magnetic domains 26 a and 26 b.This results in transfer and expansion of the record magnetic domain 22.The transferred magnetic domain 26 with the expanded magnetic domains 26a and 26 b are irradiated by laser light for reproduction through theoptical head (not shown). Thus, a state is reproduced of magnetizationwithin the reproducing layer 16, i.e. record signal.

In this manner, in the conventional magneto-optical recording mediumrecording/reproducing apparatus, irradiation of laser light is with anintensity that can cause transfer of a magnetic domain from the recordlayer into the reproducing layer.

For such a case, according to the experiments conducted by the presentinventors, when only laser light was illuminated for reproductionwithout applying an alternating magnetic field Hex, a reproduced signalobtained had a waveform as shown in FIG. 4(A). In this state, when analternating magnetic field was applied, a reproduced signal obtained hada waveform as shown in FIG. 4(B). However, the reproduced signal of FIG.4(B) is not satisfactorily high in level. Thus, there has encountered alimitation in reproducing a signal when the record density is to betried to increase.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to provide anovel apparatus and method for reproducing with a magneto-opticalrecording medium.

Another object of the invention is to provide a apparatus and method forreproducing with a magneto-optical recording medium which is capable ofincreasing the intensity of a reproduced signal.

Still another object of the invention is to provide a method forreproducing with a magneto-optical recording medium and magneto-opticaldisk apparatus which can optimally set a power level of laser light.

A reproducing apparatus according to the present invention is areproducing apparatus for a magneto-optical recording medium totransfer, during reproduction, a magnetic domain recorded within arecording layer into a reproducing layer, characterized in that amagnetic domain is transferred with expansion from the recording layerto the reproducing layer by applying alternating magnetic field to themagneto-optical recording medium in a state that the predeterminedintensity of laser light is illuminated to the magneto-optical recordingmedium.

A reproducing method according to the invention is a method ofreproducing with a magneto-optical recording medium to transfer, duringreproduction, a magnetic domain recorded within a recording layer into areproducing layer, comprising: (a) illuminating laser light with apredetermined intensity not to cause transfer of the magnetic domainfrom the recording layer to the reproducing layer; and thereafter (b)applying alternating magnetic field to the magneto-optical recordingmedium, whereby the magnetic domain is transferred with expansion fromthe recording layer to the reproducing layer.

The magneto-optical recording medium is formed with a particular region,for example, for each sector or zone. This particular region ispreviously formed with a signal to adjust an intensity of laser light tobe illuminated to the magneto-optical recording medium through theoptical means.

In this invention, the optical means includes an intensity adjustingmeans to set a laser light intensity to a degree that the signal of theparticular region cannot be reproduced only by laser light. Laser lightthus adjusted in intensity is illuminated through the optical means tothe magneto-optical recording medium. Thereafter, a magnetic fieldapplying means applies magnetic field to the magneto-optical recordingmeans. As a result, the record magnetic domain recorded in the recordinglayer of the magneto-optical recording medium is transferred withexpansion to the reproducing layer. That is, if alternating magneticfield is applied in a state that laser light is illuminated with anintensity at which no transfer of the record magnetic domain can becaused to the reproducing layer, there occur concurrent transfer andexpansion of the record magnetic domain to the reproducing layer. As aresult, the record magnetic domain is transferred with expansion.

According to this invention, because transfer and expansion of amagnetic domain is effectively made from the recording layer to thereproducing layer, a reproduced signal is increased in level.Consequently, the record magnetic domain in the recording layer can bereduced in size, enabling recording with higher density.

A second reproducing method according to the invention is a method ofreproducing a signal from a magneto-optical recording medium by usinglaser light and an alternating magnetic field, including a first stepand a second step. In the first step, a power level of laser light isdetermined based on a reproduced signal obtained by reproducing from themagneto-optical recording medium with using laser light and alternatingmagnetic field, and on a record signal. In the second step, a signal isreproduced from the magneto-optical recording medium by using the laserlight set at a power level determined by the first step and analternating magnetic field.

According to the second reproducing method, the record signal recordedin the magneto-optical recording medium is reproduced by magnetic domainexpansion so that a power level of laser light is determined based onthe reproduced signal and record signal. It is therefore possible toaccurately determine a power level. Further, magnetic domain expansionand reproduction can be made suited for a loaded magneto-opticalrecording medium.

A third reproducing method according to the invention is a method forreproducing a signal from a magneto-optical recording medium by usinglaser light and alternating magnetic field, including a first step, asecond step, a third step and a fourth step. In the first step, apredetermined record signal is recorded to the magneto-optical recordingmedium. In a second step, the signal recorded in the first step isreproduced while changing a power level of laser light. In the thirdstep, a signal reproduced in the second step is compared with the recordsignal and determining a power level of laser light at which thereproduced signal is substantially coincident with the record signal. Inthe fourth step, a signal is reproduced from the magneto-opticalrecording medium by using laser light set in the power level determinedin the third step and alternating magnetic field.

According to the third reproducing method, a predetermined record signalis actually recorded in a magneto-optical recording medium. A powerlevel of laser light to be illuminated is determined such that areproduced signal, obtained by performing magnetic domain expansion andreproduction on the recorded signal while changing laser light powerlevel, becomes coincident with the record signal. Accordingly, evenwhere the magneto-optical recording medium loaded is not recorded with asignal to determine a laser light power level, it is possible toaccurately determine a power level suited for the loaded magneto-opticalrecording medium. Also, accurate magnetic domain expansion andreproduction are possible using a determined power level of laser light.

A fourth reproducing method according to the invention is a method ofreproducing a signal from a magneto-optical recording medium by usinglaser light and alternating magnetic field, including a first step, asecond step, a third step and a fourth step. In the first step, apredetermined record signal is recorded in a calibration region providedin the magneto-optical recording medium. In the second step, the recordsignal is reproduced from the calibration region while changing a powerlevel of laser light, by using laser light and alternating magneticfield. In the third step, a signal reproduced in the second step iscompared with the record signal and determining a power level of laserlight at which the reproduced signal is substantially coincident withthe record signal. In the fourth step, a signal is reproduced from themagneto-optical recording medium by using laser light set in the powerlevel determined in the third step and alternating magnetic field.

According to the fourth reproducing method, the magneto-opticalrecording medium has a calibration region. The calibration region isactually recorded with a predetermined record signal so that magneticexpansion and reproduction is made on the recorded signal to determine apower level of laser light for signal reproduction. Accordingly, a powerlever of laser light to be illuminated for reproduction can bedetermined without using a region to be recorded with a signal. Also, ifa calibration region is placed such that laser light reaches a usualsignal recorded region after passing the calibration region, it ispossible to determine a power level of laser light to be illuminatedprior to reproducing the usual signal. Furthermore, where a plurality ofcalibration regions are provided in a radial direction of themagneto-optical recording medium, even if the magnetic material beuneven in magnetic characteristic over a disk substrate, magnetic domainexpansion and reproduction can be implemented in a manner suited for themagnetic characteristic.

Incidentally, in the third and fourth reproducing methods, the change inlaser light power level in the second step is desirably performed withina range that no magnetic domain transfer is made only by laser lightfrom the recording layer to the reproducing layer. By doing so, a laserlight power level is determined within a range that no magnetic domaintransfer is made only by laser light from the recording layer to thereproducing layer. It is therefore possible to accurately determine apower level suited for magnetic domain expansion and reproduction.

A magneto-optical disk apparatus according to the invention is amagneto-optical disk apparatus for recording and/or reproducing a signalto and/or from a magneto-optical recording medium by using laser lightand magnetic field, comprising: a determination circuit for determininga power level of laser light based on a predetermined record signal anda signal reproduced of the predetermined record signal from themagneto-optical recording medium by using laser light and alternatingmagnetic field.

In this magneto-optical disk apparatus, the determination circuitdetermines a power level of laser light based on a signal reproducedusing laser light and alternating magnetic field as well as a recordsignal as a basis of the reproduced signal. Accordingly, it is possibleto promptly and accurately determine whether the reproduced signal iscorrect or not. As a result, a laser light power level can be determinedwith rapidity and accuracy.

A second magneto-optical disk apparatus according to the invention is amagneto-optical disk apparatus for recording and/or reproducing a signalto and/or from a magneto-optical recording medium by using laser lightand magnetic field, comprising: a determination circuit for determininga power level of laser light based on the reproduced signal whilechanging the power level of laser light such that a signal produced ofthe record signal becomes substantially coincident with the recordsignal.

According to the second magneto-optical disk apparatus, the loadedmagneto-optical recording medium is previously recorded with a signal todetermine a laser light power level suited for magnetic domain expansionand reproduction. The recorded signal is reproduced by magnetic domainexpansion while changing the laser light power level. If the power oflaser light is too intense or weak, there is no agreement between thereproduced signal and the record signal. The determination circuitdetermines, as an optimal laser light power level, a power level thatthe reproduced signal substantially agrees with the record signal. It istherefore possible to determine an optimal laser light power lever withrapidity. Thus, a power level can be determined suited for the loadedmagneto-optical recording medium.

A third magneto-optical disk apparatus according to the invention is amagneto-optical disk apparatus for recording and/or reproducing a signalto and/or from a magneto-optical recording medium by using laser lightand magnetic field, comprising: an optical head, a magnetic head and adetermination circuit. The optical head illuminates laser light to themagneto-optical recording medium and detects reflection light thereof.The magnetic head applies magnetic field to the magneto-opticalrecording medium. The determination circuit determines a power level oflaser light based on a record signal in the magneto-optical recordingmedium and a reproduced signal of the record signal detected by theoptical head while applying alternating magnetic field through themagneto-optical head and changing a power level of laser light, so thatthe reproduced signal becomes substantially coincident with the recordsignal.

According to the third magneto-optical disk apparatus, the alternatingmagnetic field for determining a laser light power level is appliedthrough the magnetic head to the magneto-optical recording medium whilelaser light is illuminated through the optical head to themagneto-optical recording medium. Even in a structure having a magnetichead and an optical head arranged sandwiching the magneto-opticalrecording medium, a laser light power level suited for magnetic domainexpansion and reproduction can be determined with rapidity and accuracy.

A fourth magneto-optical disk apparatus according to the invention is amagneto-optical disk apparatus for recording and/or reproducing toand/or from a magneto-optical recording medium by using laser light andmagnetic field, comprising an optical head, a laser drive circuit, amagnetic head and a determination circuit. The optical head illuminateslaser light to the magneto-optical recording medium and detectsreflection light thereof. The laser drive circuit drives a laser lightsource included in the optical head. The magnetic head applies magneticfield to the magneto-optical recording medium. The determination circuitoutputs a drive signal to the laser drive circuit to change a powerlevel of laser light to be emitted through the optical head, anddetermines a power level of laser light based on a predetermined recordsignal recorded to the magneto-optical recording medium, alternatingmagnetic field applied through the magnetic head and a signal reproducedof the record signal detected by laser light emitted through the opticalhead based on the drive signal, so that the reproduced signal becomessubstantially coincident with the record signal.

According to the fourth magneto-optical disk apparatus, a drive signalis outputted from the determination circuit to the laser drive circuit,to change a power level of laser light to be emitted through the opticalhead. Based on the drive signal, the laser drive circuit drives a laserlight source included in the optical head so that laser light differentin power level is illuminated to the magneto-optical recording medium.Consequently, a reproduced signal can be detected by performing magneticdomain expansion and reproduction while changing the power level on themagneto-optical recording medium. Based on the reproduced signal, apower level of laser light is determined. As a result, it is possible toaccurately determine a laser light power level.

A fifth magneto-optical disk apparatus according to the invention is amagneto-optical optical disk apparatus for recording and/or reproducinga signal to and/or from a magneto-optical recording medium by usinglaser light and magnetic field, comprising an optical head, a laserdrive circuit, a magnetic head, a magnetic head drive circuit and adetermination circuit. The optical head illuminates laser light to themagneto-optical recording medium and detecting reflection light thereof.The laser drive circuit drives laser light source included in theoptical head. The magnetic head applies magnetic field to themagneto-optical recording medium. The magnetic head drive circuit drivesthe magnetic head. The determination circuit outputs to the magnetichead drive circuit a first drive signal to record a predetermined recordsignal in the magneto-optical recording medium and to the laser drivecircuit a second drive signal to change a power level of laser light tobe emitted through the optical head, and determines a power level oflaser light based on a predetermined record signal recorded based on thefirst drive signal, alternating magnetic field applied through themagnetic head, and a signal reproduced of the record signal detected bylaser light emitted through the optical head based on the second drivecircuit, so that the reproduced signal becomes substantially coincidentwith the record signal.

According to the fifth magneto-optical disk apparatus, the determinationcircuit outputs to the magnetic drive circuit a first drive signal torecord a predetermined record signal for determining a laser light powerlevel. Based on the first drive signal, a predetermined record signal isrecorded on the magneto-optical recording medium. Also, thedetermination circuit output to the laser drive circuit a signal tochange the laser light power level. The laser drive circuit drives alaser light source in the optical head based on the second drive signal.Thus, laser light different in power level is illuminated to themagneto-optical recording medium, reproducing the predetermined recordsignal through magnetic domain expansion. Accordingly, even where theloaded magneto-optical recording medium is previously not recorded witha predetermined record signal, it is possible to rapidly and accuratelydetermine a laser light power level suited for the loadedmagneto-optical recording medium.

In the fifth magneto-optical disk apparatus, the determination circuit,after loading the magnet-optical recording medium, outputs to themagnetic head drive circuit a first drive signal to record apredetermined record signal for determining a laser light power levelafter loading the magneto-optical recording medium but before recordingthe record signal, and to the laser drive circuit a second drive signalto change the power level of laser light to be emitted through theoptical head before reproducing the record signal. By doing so, prior torecording a usual signal, a first drive signal is outputted from thedetermination circuit to the magnetic head drive circuit to record thepredetermined record signal for determining a laser light power level.Based on the first drive signal, the predetermined record signal isrecorded on the magneto-optical recording medium. Also, a second signalis outputted from the determination circuit to the laser drive circuitto change the laser light power level. Magnetic domain expansion andreproduction is made on the predetermined record signal already recordedwhile changing the laser light power level. Based on a signalreproduced, a laser light power level is determined. Accordingly, it ispossible to positively determine a laser light power lever suited formagnetic domain expansion and reproduction before reproduce operation onthe usual signal. Thus, the usual signal can be accurately effected ofmagnetic domain expansion and reproduction.

The above described objects and other objects, features, aspects andadvantages of the present invention will become more apparent from thefollowing detailed description of the present invention when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional illustrative view showing one example of amagneto-optical recording medium used in the present invention;

FIG. 2 is an illustrative view showing a conventional method toreproduce a record magnetic domain recorded in a recording layer of themagneto-optical recording medium of FIG. 1, wherein FIG. 2(A) is beforeexpansion while FIG. 2(B) is after expansion;

FIG. 3 is an illustrative view showing a spot and temperaturedistribution of laser light illuminated during reproducing with themagneto-optical recording medium;

FIG. 4 is a waveform diagram showing examples of reproduced signalsrespectively obtained in stages of transfer and expansion in the priorart of FIG. 2, wherein FIG. 4(A) shows one of during transfer and FIG.4(B) is one of during expansion;

FIG. 5 is a block diagram showing one embodiment of the invention;

FIG. 6 is a circuit diagram showing an example of laser drive circuit inthe FIG. 5 embodiment;

FIG. 7 is an illustrative view showing an example in arrangement of aparticular region for laser light magneto-optical recording mediumintensity adjustment formed on a disk;

FIG. 8 is an illustrative view showing another embodiment in arrangementof a particular region;

FIG. 9 is an illustrative view showing still another example inarrangement of a particular region;

FIG. 10 is an illustrative view showing a further example in arrangementof particular region;

FIG. 11 is an illustrative view showing an external magnetic field(pulses) to be outputted through a magnetic head during forming aparticular region;

FIG. 12 is an illustrative view showing a record magnetic domain formedin a particular region of a recording layer;

FIG. 13 is a flowchart showing an intensity adjustment mode in the FIG.5 embodiment;

FIG. 14 is a graph representing that the reproduced signal is changed inlevel depending upon change in intensity of laser light in the FIG. 5embodiment;

FIG. 15 is an illustrative view representing that the record magneticdomain in the recording layer is expanded and transferred to thereproducing layer in the FIG. 5 embodiment, wherein

FIG. 15(A) shows that no transfer is made in a state of merelyilluminating laser light while

FIG. 15(B) shows that expansion and transfer are effected by applying analternating magnetic field;

FIG. 16 is a waveform diagram showing an alternating magnetic field tobe applied to a disk through a magnetic head;

FIG. 17 is a waveform diagram showing a reproduced signal obtained inthe FIG. 5 embodiment;

FIG. 18 is a timing chart showing operation of an external sync signalcreating circuit in the FIG. 5 embodiment;

FIG. 19 is a block diagram showing a magneto-optical disk apparatusaccording to another embodiment of the invention;

FIG. 20 is an illustrative view showing a principle of magnetic domainexpansion and reproduction similar to FIG. 2;

FIG. 21 is an illustrative view showing a method to optimize laser lightpower;

FIG. 22 is an illustrative view showing in plan a magneto-opticalrecording medium;

FIG. 23 is an illustrative view showing in plan tracks formed on themagneto-optical recording medium;

FIG. 24 is an illustrative view showing to create an external syncsignal;

FIG. 25 is a flowchart showing a reproducing method using magneticdomain expansion in the FIG. 19 embodiment;

FIG. 26 is a flowchart showing another reproducing method using magneticdomain expansion in the FIG. 19 embodiment;

FIG. 27 is a flowchart showing still another reproducing method usingmagnetic domain expansion in the FIG. 19 embodiment; and

FIG. 28 is a flowchart showing another reproducing method using magneticdomain expansion in the FIG. 19 embodiment.

BEST FORM FOR PRACTICING THE INVENTION

Referring to FIG. 5, an apparatus 30 for recording/reproducing with amagneto-optical recording medium in this embodiment includes a spindlemotor 32 to rotate a magneto-optical recording medium, or disk, 10. Thespindle motor 32 is controlled by a servo circuit 34. A magnetic head 36is provided above the magneto-optical recording medium, or disk, 10which is not in contact with the disk 10. At an underneath of the disk,an optical head 38 is provided similarly. The magnetic head 36, ashereinafter referred to, is utilized not only to form a record magneticdomain 22 (FIG. 2) in a recording layer 14 (FIG. 1) of the disk 10 butalso to apply alternating magnetic field to expand and transfer a recordmagnetic domain 22 into a reproducing layer 16. The optical head 38includes, as well known, a laser device, a light receiving element, apolarizing beam splitter and so on. The laser device (not shown) is toilluminate laser light onto the magneto-optical recording medium, ordisk, 10 during reproduction. It should be noted that in this embodimentthe intensity of laser light is set different from that of theconventional, as will be discussed later. That is, conventionally laserlight has been set to such an intensity that it by itself causestransfer of a record magnetic domain into the reproducing layer 16 asexplained before. However, this embodiment sets the intensity of laserlight to a degree that no record magnetic domain is transferred bymerely illuminating laser light to the magneto-optical recording medium10. Two light receiving elements, e.g. photo-diodes, detect respectivepolarizing axes of reflection light that differ depending upon apolarity of magnetization an expanded, transferred magnetic domainwithin the reproducing layer 16, thereby outputting a reproduced signal(RF signal).

The reproduced signal from the optical head 38 is supplied to areproduced signal amplifier circuit 40. The reproduced signal amplifiercircuit 40 supplies tracking error and focus error signals contained inthe reproduced signal to a servo circuit 34. The servo circuit 34controls the spindle motor 32 to rotate at a predetermined rotationalspeed and an objective lens (not shown) included in the optical head 38,in response to the tracking and focus signals as well as a clock signal(hereinafter stated). That is, servo circuit 34 performs tracking servoand focus servo.

The reproduced signal having been amplified by the reproduced signalamplifier circuit 40 is passed through a low-pass filter 42 and thendelivered to a PLL (Phase-Locked Loop) 44, i.e. as clock creatingcircuit, and to a decoder 46. The PLL 44 adjusts the phase and frequencyof an oscillation clock depending upon a phase comparison between areproduced clock contained in the reproduced signal and an oscillationclock given from the VCO (Voltage-Controlled Oscillator: not shown),thus outputting an oscillation clock as a system clock. The system clockis given to the servo circuit 34 as stated above and to a controlcircuit 48 and decoder 46. The decoder 46 decodes an output signal(reproduced signal) from the low-pass filter 42 according to the clock,and outputs reproduced data.

The control circuit 48 under control of a microcomputer 50 controls themagnetic head drive circuit 52 and laser drive circuit 54. The magnetichead drive circuit 52 includes a pulse signal source (not shown) togenerate a pulse signal for writing a record magnetic domain into therecording layer 14 (FIG. 1) through the magnetic head 36, and analternating current signal source (not shown) to generate an alternatingmagnetic field through the magnetic head 36. That is, the controlcircuit 48 is given modulated record data from a modulator 56. Thecontrol circuit 48 supplies a signal to magnetic head drive circuit 52,according to the modulated record data. In response, the magnetic headdrive circuit 52 controls the pulse signal source, and supplies drivesignal to the magnetic head 36 so that a record magnetic domain can berecorded in the recording layer of the magneto-optical recording medium,or disk, 10 in according with the record data. Incidentally, thealternating current signal outputted by the alternating current source,i.e. an alternating magnetic field, has a frequency, for example, of 2.0MHz in this embodiment. However, it should be noted that the frequencycan be arbitrarily varied.

The laser drive circuit 54 includes, as concretely shown in FIG. 6, aplurality of resistors R1, R2, R3, . . . connected in series between apower source Vcc and a ground. The resistors R1, R2, R3, . . . hasseries connection points connected with respective fixed contacts S1,S2, S3, . . . of a switch 542. The switch 542 has a movable contactswitch that is switched to any of the fixed contacts S1, S2, S3, . . .according to a switch signal given from the control circuit 48.Accordingly, the switch 542 at its movable contact C outputs a differentvoltage depending upon which fixed contact the movable contact isconnected to. The output voltage of the switch 542 is given to a base ofa transistor 544 through an amplifier 543. A laser device 545 isconnected between a collector of the transistor 544 and the powervoltage Vcc while an emitter of the transistor 544 is ground through anemitter resistance.

In this laser drive circuit 54, the movable contact C of the switchingof the switch 542 if switched by the control circuit 48 causes change ofan output voltage of the amplifier 543, i.e. a base voltage of thetransistor 544, thereby changing a drive current to the laser device545. Accordingly, it is possible to adjust an output of laser lightemitted by the laser device 545.

Meanwhile, the reproduced signal passed via the low-pass filter 42 isfurther delivered to the microcomputer 50. The microcomputer, as will bediscussed later, controls the laser drive circuit 54 to set the power orintensity of laser light depending upon whether a reproduced signal isobtained from the low-pass filter 42 or not.

For the recording/reproducing apparatus 30 of this embodiment, aparticular region 11 is formed on the magneto-optical recording medium,or disk, 10 as shown in FIG. 7 to FIG. 10. The particular region 11 isto adjust a laser light output by reproducing a record signal out of thesame region. It should be noted that it is possible for a reproductionexclusive apparatus without having recording function to utilize amagneto-optical recording medium or disk previously formed with such aparticular region.

In the FIG. 7 embodiment, a particular region 11 is formed in a positionimmediately following a TOC region provided on an outer peripheral sideof the disk 10. In an embodiment of FIG. 8, a particular region 11 isformed in an end position of the disk 10. In an embodiment of FIG. 9,particular regions 11 are formed in respective positions of immediatelyfollowing a TOC region and an end of the disk 10. In an embodiment ofFIG. 10, particular regions 11 are set in respective beginning positionsof zones. That is, the particular regions 11 are formed for each zone orsector.

By utilizing a disk 10 formed with such a particular region 11, theadjustment of laser light intensity can be implemented at arbitrarytiming. For example, it is possible to conduct adjustment on intensityto determine an optimized output of laser light at initializing thedisk. Or otherwise, laser light intensity adjustment can be performed ata time at the disk 10 is loaded on a recording/reproducing apparatus orreproducing apparatus. In particular, if the disk of FIG. 10 isutilized, the laser light output can be optimized each time reproductionis effected for each zone.

Now explained is a method to form a particular region 11 based on theFIG. 5 embodiment. When forming a particular region, the microcomputer50 sets a test signal record mode. In this mode the microcomputer 50provides an instruction signal to the control circuit 48 to output atest signal. The control circuit 48, in turn, enables a pulse signalsource (not shown) of the magnetic head drive circuit 52. Consequently,the magnetic head drive circuit 52 supplies a pulse signal as shown inFIG. 11 to the magnetic head 36. That is, the magnetic head 36 appliesan external magnetic field onto the disk 10 in response to anintermittent pulse signal as shown in FIG. 11. Consequently, recordmagnetic domains 22 are formed in the recording layer 14 (FIG. 1) of thedisk 10, as shown in FIG. 12. The record magnetic domain 22 has a sizecorresponding to a minimum magnetic domain with whichrecording/reproducing is possible on the disk. The interval of therecord magnetic domains 22 is selected greater than a spot diameter 24 a(FIG. 2) of laser light 24. That is, the test signal magnetic domainsrecorded in the recording layer 14 at a particular region 11 areisolated magnetic domains having an interval greater than a laser lightspot diameter. Incidentally, in the FIG. 11 embodiment the recordmagnetic domains has a size, for example, of approximately 0.1-0.2 μmand an interval set, for example, equal to or longer than 0.8 μm.

Now an intensity adjustment mode is explained with reference to FIG. 13and FIG. 14, wherein the laser light output is optimized using a disk 10formed with a particular region 11 (FIG. 7 to FIG. 10). FIG. 14 is agraph showing a relationship between a laser light intensity and areproduced signal. In the embodiment the laser light intensity is set toan intensity B around which no reproduced signal is obtainable in FIG.14.

In the intensity adjustment mode, if disk 10 is loaded, themicrocomputer 50 in the first step S1 disables the magnetic head 36. Themicrocomputer 50 in the next step S2 performs initial setting on anoutput Pr of laser light 24. Although the output initial value is setfor example at approximately 0.6 mW, it is possible to arbitrarily setthe initial value.

After setting an initial value as above, the microcomputer 50 in step S3performs production on a test signal magnetic domain recorded asdescribed above in the particular region 11 (FIG. 7 to FIG. 10). Thatis, the microcomputer 50 enables the laser drive circuit 54 through thecontrol circuit 48 similarly to usual reproduction, to drive the laserdevice 545 (FIG. 6) with the initial power set in the former step S2.Due to drive to the laser device 545, laser light 24 (FIG. 3) isoutputted from the optical head 38. Then, the microcomputer 50 in stepS4 determines whether a reproduced signal was obtained, based on asignal given from the low-pass filter 42.

If there was no reproduced signal, in step S5 the flag is set to “0”. Inthe succeeding step S6 it is determined whether the preceding flag was“1” or not. When the flag in the preceding time was not “1”, i.e. whenno reproduced signals were successively detected, in step S7 a switchsignal is given to the switch 542 of the laser drive circuit 54 in orderto increase the laser light output, specifically to decrease theresistance value of the FIG. 6 circuit. Then, returning again to thestep S3, the microcomputer in step S4 detects on the presence or absenceof a reproduced signal in a manner similarly to the above.

Where there is a reproduced signal, the flag is set to “1” in step S8,and in the succeeding step S9 a switch signal is given to the switch 542of the laser drive circuit 54 to reduce the laser light output.Returning again to the step S3, the microcomputer in step S4 detects onthe presence or absence of a reproduced signal, similarly to the above.

In the case that no reproduced signal is detected after obtaining areproduced signal, “YES” is determined in the step S6. Accordingly, thelaser light intensity at that time is set as an optimal power.

Referring to FIG. 14, when the laser light intensity becomes a certainvalue, the reproduced signal is increased in level. However, the laserlight intensity if excessively high results in decrease in thereproduced signal level. This is because the temperature of themagneto-optical recording medium 10 is brought close to the Curie pointdue to intensive laser light and the reproducing layer 16 is reduced incoercivity.

In FIG. 14, when the laser light with intensity denoted at a point A isilluminated, the reproduced signal is high in level. Accordingly, inthis case it can be understood that transfer of a record magnetic domainoccurs to the reproducing layer 16. Meanwhile, because at a point B noreproduced signal is obtained, no transfer of a magnetic domain occursto the reproducing layer. In this embodiment the laser light intensityis set to the point B according to the flowchart of FIG. 13 explainedabove. Setting is within a range of 80 to 100% with the power at thepoint B taken as a reference.

Explanation is made on a case to practically reproduce a record signalafter adjusting the laser light intensity as described above. As wasexplained before, the laser light intensity is set to an intensity thatthe intensity itself cannot cause transfer of a magnetic domain from therecording layer to the reproducing layer 16. In this case, no magneticdomain to be reproduced is formed in the reproducing layer as shown inFIG. 15(A) only by illuminating laser light onto the magneto-opticalrecording medium, or disk 10. Thus no reproduced signal is outputted. Ifin the state the magnetic head drive circuit 52 is enabled by themicrocomputer 50, i.e. by the control circuit 48, an alternatingmagnetic field Hex as shown in FIG. 16 is applied to the magneto-opticalrecording medium, or disk 10, through the magnetic head 36. Accordingly,when the alternating magnetic field Hex is in a particular polarity, arecord magnetic domain recorded in the recording layer 14 is transferredwith expansion into the reproducing layer 16 as shown in FIG. 15(B),thus forming an expanded transferred magnetic domain 26′.

Consequently, a reproduced signal as shown in FIG. 17 is outputted fromthe reproduced signal amplifier circuit 40 of FIG. 5, i.e., from thelow-pass filter 42. Referring to FIG. 17, it can be understood that thereproduced signal obtainable at this time is significantly increased inlevel as compared to the prior art reproduced signal as shown in FIG.4(B).

If the alternating magnetic field changes to the other polarity as shownin FIG. 16, the magnetic domain having been transferred with expansionto the reproducing layer 16 is erased. Due to this, in FIG. 17 thereproduced signal becomes a pulse form. Incidentally, the respectivetimes T1 and T2 of the alternating magnetic field polarities, shown inFIG. 16, may not necessarily be equal in ratio to each other. It ispossible to set a duty ratio of optimal times T1 and T2 in accordancewith the characteristics of the magneto-optical recording medium 10.

In this manner, in the present embodiment the intensity of laser lightis set to an extent that no magnetic domain in the recording layer 14 istransferred into the reproducing layer 16. Due to this, if analternating magnetic field Hex is applied, the record magnetic domain isexpanded and transferred to the reproducing layer 16, thus providing ahigh level reproduced signal. As a result, the signal even if recordedin a small domain can be reproduced with a sufficiently high level,increasing record intensity as compared to the conventional.

Now explanation is made on the timing of driving to the optical head 38and the magnetic head 36. As shown in FIG. 18(A), the magneto-opticalrecording medium, or disk 10 is formed thereon with a land/grooveschemed track 60. The track 60 has discontinuous regions 62 formed at apredetermined interval without having lands/grooves. For thediscontinuous region 62, the optical head 38, i.e. the reproduced signalamplifier circuit 40, outputs a signal as shown in FIG. 18(B). Thissignal is delivered to the external synchronization signal creatingcircuit 58. The external sync signal creating circuit 58 compares, by acomparator (not shown), the reproduced signal with a reference voltage,thereby outputting a pulse signal as shown in FIG. 18(C). This pulsesignal is supplied to the control circuit 48. The control circuit 48, inturn, supplies a pulse signal as shown in FIG. 18(E) to the laser drivecircuit 54 and magnetic head drive circuit 52, in synchronism with thesystem clock given from the PLL 44 shown in FIG. 18(D) as well as theabove-mentioned pulse signal. Laser may be by DC drive, or otherwise bypulse illumination wherein during a high level of the pulse signal thelaser drive circuit 54 drives the laser device (not shown) of theoptical head 36 that laser light controlled in output is intermittentlyilluminated through the optical head 38 onto the magneto-opticalrecording medium 10. However, no transfer of record magnetic domainoccurs to the reproducing layer.

In response to the pulse signal of FIG. 18(E), the magnetic head drivecircuit 52 drives magnetic head 36 to apply an alternating magneticfield as was shown in FIG. 16 onto the magneto-optical recording medium,or disk, 10. At this time, transfer with expansion of a record magneticdomain occurs to the reproducing layer, thus providing a reproducedsignal.

Incidentally, in the embodiment the reproduced layer used a magneticlayer which assumes a perpendicular magnetic anisotropy film within arange of from room temperature to the reproducing temperature. However,the reproducing layer may be such a magnetic layer that assumes a planemagnetic anisotropy film at normal temperature and a perpendicularmagnetic anisotropy film at elevated temperature. In this case, theremay be a case that the application of an alternating external magneticfield be unnecessary for magnetic domain expansion.

Referring to FIG. 19, a magneto-optical disk apparatus 30 according toanother embodiment of the invention includes components similar to thoseof the FIG. 5 embodiment. Therefore, the components same as or similarto those of FIG. 5 are denoted by the same reference characters,omitting duplicated explanations hereinunder.

A magneto-optical disk apparatus 30 of FIG. 19 includes an optical head38. This optical head 38 has a laser device 545 to illuminate a wavelength of 635 (allowable error ±35, hereinafter the same) nm of laserlight onto a magneto-optical recording medium 10 similarly to the FIG. 5embodiment, and detects the reflection light therefrom.

A reproduced signal amplifier circuit 40 amplifies a focus error signal,tracking error signal, optical signal and magneto-optical signaldetected by the optical head 38 to predetermined level, and then outputsthe focus error and tracking error signals to a servo circuit 34, theoptical signal to an external sync signal creating circuit 58 andmagneto-optical signal to a waveform shaper 60. The waveform shaper 60includes LPF 42 that is same as that of the FIG. 5 embodiment, and cutsthe input magneto-optical signal of noise and converts an analog signalinto a digital signal. The digital signal is outputted to decoder 46 anddetermination circuit 62.

The external sync signal creating circuit 58 creates an external syncsignal according to a method hereinafter described based on the outputoptical signal, and outputs it to the servo circuit 34, the decoder 46,the laser drive circuit 54 and the magnetic head drive circuit 52.

The servo circuit 34 controls a servo mechanism 64 based on the inputfocus error and tracking error signals and causes a spindle motor 32 torotate at a predetermined rotational speed in synchronism with theinputted external sync signal. This servo mechanism 64 performs trackingservo and focus servo for an objective lens (not shown) included in theoptical head 38, based on the focus error and tracking error signals.

Incidentally, an encoder 66 encodes record data and outputs it to amodulation circuit 56. The modulation circuit 56 modulates the recordsignal to a predetermined scheme. Where signal record is made by amagnetic field modulation scheme, the modulation circuit 56 outputs amodulated record signal to the magnetic head drive circuit 52. Whererecording is by an optical modulation scheme, the modulation circuitoutputs the modulated record signal to the laser drive circuit 54.

The determination circuit 62 inputs a digitized magneto-optical signalfrom the waveform shaper 60 and determines by a method hereinafterdescribed whether the digitized magneto-optical signal substantiallyagrees with the record signal or not, thereby determining laser lightpower suited for magnetic domain reproduction with expansion.Incidentally, although the determination circuit 62 may be structured asa discrete component, preferably it is formed as a part of themicrocomputer 50 function of FIG. 5 embodiment.

Although the principle of magnetic domain expansion and reproductionwere explained before with reference to FIG. 2, it is again explainedwith reference to FIG. 20. A magneto-optical recording medium 10includes a recording layer 14, an intermediate or non-magnetic layer 18and a reproducing layer 16. In the case of effecting magnetic domainexpansion and reproduction, the reproducing layer 16 is initiallymagnetized in one given direction (see FIG. 20(A)).

When performing magnetic domain expansion and reproduction, themagneto-optical recording medium 10 is illuminated by laser light 24from a side of the reproducing layer 16 and applied by an alternatingmagnetic field Hex from a side of the recording layer 14 (see FIG.20(B)).

Thereupon, the recording layer 14 at a region of a magnetic domain 22 isheated to a predetermined temperature or higher by the laser light 24.The magnetic domain 22 is transferred with expansion into thereproducing layer 16 through the intermediate or non-magnetic layer 18by static magnetic coupling in timing that a same direction of amagnetic field as that of magnetization of the magnetic domain 22 isapplied due to the alternating magnetic field Hex. Thus, an expandedmagnetic domain 23 magnetized in the same direction as that of themagnetic domain 22 comes into existence in the reproducing layer 16 (seeFIG. 20(C)). The laser light 24 illuminated on the reproducing layer 16is rotated in its polarizing plane and reflected thereon due to themagnetization of the magnetic domain 23. The detection of the reflectionlight enables reproduction of a signal having been recorded as themagnetic domain 22.

After ending the detection of the magnetic domain 23 due to the laserlight 24, a magnetic field is applied in a opposite direction to themagnetization of the magnetic domain 23 whereby the magneto-opticalrecording medium 10 returns to the initial state (FIG. 20(A)) toreproduce a next magnetic domain in the similar manner.

In the magnetic domain expansion and reproduction as explained withreference to FIG. 20, the power of laser light is extremely importantthat is to be illuminated to a magneto-optical recording medium 10. Fromthis point of view, in the embodiment as was explained with reference toFIG. 5, magnetic domain expansion and reproduction were made byilluminating to the magneto-optical recording medium 10 the laser lighthaving such an intensity that cannot cause transfer of a magnetic domainfrom the recording layer into the reproducing layer only by the laserlight illumination.

However, it has been revealed from a continuous study conducted by thepresent inventors that, even where illuminating laser light having powerof within the above-mentioned range, there is a case that a magneticdomain in the recording layer 14 be not accurately transferred withexpansion to the reproducing layer 16 as the power may be.

FIG. 19 shows an embodiment for providing a method that determines laserlight power to cause accurate transfer with expansion of a magneticdomain of the recording layer 14 to the reproducing layer 16 andreproducing the magnetic domain of recording layer 14 based on thedetermined laser light power by magnetic domain expansion, and amagneto-optical disk apparatus using that method.

Referring to FIGS. 19 and 21, a magneto-optical recording medium 10 isloaded on the magneto-optical disk apparatus 30. If established is astate that signal recording onto the magneto-optical recording medium 10is possible by a usual method, the determination circuit 62 outputs tothe magnetic head drive circuit 52 a drive signal (B) (also referred toas “first drive signal”) made by binalizing a predetermined recordsignal (A) (see FIG. 21). The magnetic head drive circuit 52 drives themagnetic head 36 based on the drive signal (B) inputted in synchronismwith an external sync signal (k) given from the external sync signalcreating circuit 58. A magnetic field is applied to the magneto-opticalrecording medium 10, based on the drive signal (B) give from themagnetic head 36 whereby the predetermined record signal (A) is decodedon the magneto-optical recording medium 10. In this case, the laserdrive circuit 54 drives the laser light source 545 to thereby illuminatea predetermined intensity of laser light to the magneto-opticalrecording medium 10 through the optical head 38.

After ending to record the predetermined record signal (A), the power oflaser light is changed to reproduce the predetermined recorded signal(A). In this case, the determination circuit outputs a drive signal (c)to the magnetic head drive circuit 52 and a drive signal (e) (alsoreferred to as “second drive signal”) to the laser drive circuit 54. Thedrive signal (c) is to create an alternating magnetic field, while thedrive signal (e) is to change the power of laser light to be irradiatedthrough the optical head 38. The magnetic head drive circuit 52 drivesthe magnetic head based on the drive signal (c) to apply an alternatingmagnetic field (d) to the magneto-optical recording medium 10 throughthe magnetic head 36. On the other hand, the laser drive circuit 54drives the laser light source 545 based on the drive signal (e) whereby3 kinds of laser light different in power level are illuminated for agiven duration to the magneto-optical recording medium 10 through theoptical head 38.

In the case where the laser light source 545 is driven based on signal(e1) of the drive signal (e) to illuminate laser light onto themagneto-optical recording medium 10 through the optical head 38, amagneto-optical signal (f1) is detected. Also, where the laser lightsource 545 is driven based on a signal (e2) to illuminate laser light tothe magneto-optical recording medium 10 through the optical head 38, amagneto-optical signal (f2) is detected. Further, where the laser lightsource 545 is driven based on a signal (e3) to illuminate laser light tothe magneto-optical recording medium 10 through the optical head 38, amagneto-optical signal (f3) is detected. The laser light due to drivebased on the signal (e1) has a power of 1.9 mW. The laser light due todrive based on the signal (e2) has a power of 2.0 mW. The laser lightdue to drive based on the signal (e3) has a power of 2.1 mW. These powerlevels are those in emission through the optical head 38. Also, thealternating magnetic field (d) for application has a peak intensity of±300 Oe.

The conversion of the magneto-optical signals (f1), (f2) and (f3)detected for respective ones of laser light power provides signals (g1),(g2) and (g3). The signal (g1) means “01000010”, the signal (g2)“01100010”, and the signal (g3) “01101010”. The signals “01000010” and“01101010” are different from the predetermined record signal (A) butthe signal “01100010” agrees with the predetermined record signal (A).That is, when the laser light has a power level of 1.9 mW, a signal“01000010” is detected wherein for the predetermined record signal“01100010” the third-positioned “1” is erroneously detected as “0”.Also, when the laser light has a power level of 2.1 mW, a signal“01101010” is detected wherein for the predetermined record signal“01100010” the fifth-positioned “0” is erroneously detected as “1”.Furthermore, when the laser light has a power level of 2.0 mW, a signal“01100010” is detected which agrees with the predetermined record signal“01100010”. Consequently, when the laser light is too weak in powerlevel, the signal to be detected “1” is erroneously detected as “0”.When the laser light is too intense in power level, the signal to bedetected “0” is erroneously detected as “1”.

In this embodiment, the laser light is varied in power level to performmagnetic domain expansion and reproduction so that a laser light powerat which a detected magneto-optical, or reproduced signal agrees with arecord signal is determined as a laser light power level suited formagnetic domain expansion and reproduction. In the above example, wheremagnetic domain expansion and reproduction are performed by setting thelaser light power level at 2.0 mW, the reproduced signal coincides withthe predetermined record signal (A). Therefore, the laser light power isdetermined 2.0 mW as a level suited for magnetic domain expansion andreproduction.

Referring again to FIG. 19, the magneto-optical signals (f1), (f2) and(f3) detected due to magnetic domain expansion and reproduction byvarying the laser light power level are inputted to the waveform shaper60 through the reproduced signal amplifier circuit 40. The waveformshaper 60 converts the signals (f1), (f2) and (f3) into digital signals(g1), (g2) and (g3) to be outputted to the determination circuit 62.

The determination circuit 62 determines whether or not each of the inputsignals (g1), (g2) and (g3) coincides with a signal (B) as a digitalsignal of the predetermined record signal (A), thereby detecting areproduced signal (g2) that agrees with the signal (B). If a reproducedsignal (g2) coincident with the signal (B) is detected, thedetermination circuit 62 outputs a signal (i) to the laser drive circuit54 such that the power of laser light to be emitted through the opticalhead 38 is set to a laser light power level at which the reproducedsignal has been detected. The laser drive circuit 54 drives the laseroptical source 545 based on the signal (i) so that laser light having apower level suited for magnetic domain expansion and reproduction isilluminated through the optical head 38 onto the magneto-opticalrecording medium 10. Due to this magnetic domain expansion andreproduction are effected with accuracy.

FIG. 22 illustrates a plan view of the magneto-optical recording medium10. The magneto-optical recording medium 10 has a spirally-formed track101 having a TOC region 102 provided at an outer periphery and a dataregion 103 placed following the TOC region 102. The optimization forlaser light power may be made by a calibration region 1031(corresponding to the region 11 in FIGS. 7 to 11) provided at thebeginning of the data region 103. Also, a plurality of calibrations1031, 1032 and 1033 may be formed in the data region 103 in order toimplement laser light power optimization by each of the calibrations1031, 1032 and 1033.

In the case of an ASMO, as shown in FIG. 23 a track is structured bygrooves 104 and lands 105. The grooves 104 and lands 105 arerespectively formed with discontinuous regions 106, 106, . . , and 107,107, . . . with a constant period. One continuity of grooves at oppositewalls is recorded, as wobbles 108 and 109, with address informationabout the groove and the land adjacent the groove. Accordingly, laserlight power optimization may be made in any of the preceding region 110and succeeding region 111 to the region formed with the wobbles 108 and109.

Referring to FIG. 24, explanation is made on creation of an externalsynchronization signal (k). The magneto-optical recording medium 10 has,as explained above, a track structure having grooves 104 and lands 105formed in an alternate fashion. The grooves 104 and the lands 105 isformed respectively with discontinuous regions 106, 106, . . . , and107, 107, . . . with a constant period. If laser light is illuminatedonto the track structure constructed as above, a signal (k1) is detectedby detecting an intensity of reflection light. By discriminating thesignal (k1) between a first level L1 and a second level L2, a pulsesignal (k2) is created. Further, an external sync signal (k) is createdin a form that a predetermined number of periodic signals exist betweenpulses of the pulse signal (k2).

The external sync signal (k) is created due to discontinuous regions106, 106, . . . and 107, 107, . . . on the magneto-optical recordingmedium 10. Consequently, even if a reproduced signal is missing over 1track or more, it is possible to create a sync signal in a stablefashion.

Referring to FIG. 25, explanation will be made on a flowchart on amethod for magnetic domain expansion and reproduction according to theinvention. If started in step S101, then in step S102 a first drivesignal is outputted from the determination circuit 62 to the magnetichead drive circuit 52. The first drive signal is to record apredetermined record signal (A) of FIG. 21. In step S103 a predeterminedrecord signal (A) is recorded on a calibration region based on the firstdrive signal. After recording the predetermined record signal (A), instep S104 an alternating magnetic field (d) is applied through themagnetic head 36 onto the magneto-optical recording medium 10. In stepS105 a second drive signal is outputted from the determination circuit62 to the laser drive circuit 54. The second drive signal is a signal(e) to emit different power levels of laser light through the opticalhead 38. In step S106 the laser drive circuit drives the laser lightsource 545 based on the second drive signal to illuminate differentpower levels of laser light through the optical head 38 to themagneto-optical recording medium 10. In step S107 the predeterminedrecord signal (A) is detected as magneto-optical signals (f1), (f2) and(f3) from the calibration region by the respective power levels of laserlight. The detected magneto-optical signals (f1), (f2) and (f3) areconverted into digital signals (g1), (g2) and (g3) and then inputted instep S108 to the determination circuit 62. Determination circuit 62compares the input digital signals (g1), (g2) and (g3) with a digitalsignal (B) of the predetermined record signal (A), thereby detecting thedigital signal (g2) coincident with the digital signal (B). In step S109the laser light power level with which the digital signal (g2) wasdetected is determined as an optimal power level for magnetic domainexpansion and reproduction.

If an optimal laser light power level has been determined, then in stepS110 setting is made, to the determined power level, the power level ofthe light to be emitted through the optical head 38 to the determinedpower level. In step S111 magnetic domain expansion and reproduction arecarried out. In step S112 the operation of signal reproduction is ended.

The flowchart of FIG. 25 shows the operation that the loadedmagneto-optical recording medium is not previously recorded with apredetermined record signal (A). However, in the case that themagneto-optical recording medium is previously recorded with apredetermined record signal (A), signal reproduction is made due tomagnetic field expansion based on a flowchart shown in FIG. 26.

The flowchart shown in FIG. 26 is a flowchart which omits the steps S102and S103 from the flowchart of FIG. 25. Other steps are the same asthose of the flowchart of FIG. 25, omitting the explanations.

Meanwhile, in the flowchart of FIG. 25, the determination circuit 62when changing in 3 stages the laser light power level outputs once adrive signal to the laser drive circuit 54. However, the invention isnot limited to this manner. That is, as shown in FIG. 27, magneticdomain expansion and reproduction may be made and then the laser lightsource 545 be driven by a second level of power to effect magneticdomain expansion and reproduction by applying that power level. That is,the steps S101 to S104 are the same as those of FIG. 25. In step S155the determination circuit 62 outputs a drive signal to the laser drivecircuit 54 such that a first power level of laser light is emittedthrough the optical head 38. In step S166 the optical head 38illuminates a first power level of laser light onto the magneto-opticalrecording medium 10, and in step S177 magnetic domain expansion andreproduction are carried out on the calibration region with the firstpower level of laser light. Thereafter, the process returns to the stepS155 where the discrimination circuit 62 outputs drive signal to thelaser drive circuit 54 such that a second power level of laser light isemitted through the optical head 38. Thereafter, the steps S166 and S177are executed similarly to the above, and the process returns to the stepS155. Then the power of laser light is set to a third power level toeffect magnetic domain expansion and reproduction.

After ending the magnetic domain expansion and reproduction with changeof laser light power, the process moves to a step S108 to effectmagnetic domain expansion and reproduction in the same manner as that ofFIG. 25.

FIG. 27 is on the case that the magneto-optical recording medium is notpreviously recorded with a predetermined record signal to optimize thelaser light power level. Meanwhile, for a case that the magneto-opticalrecording medium is previously recorded with predetermined recordsignal, magnetic domain expansion and reproduction are made by certainpower level of laser light and then the power level is changed forreproduction, as shown by a flowchart of FIG. 28.

This embodiment is characterized by determining an optimal power levelof laser light for magnetic domain expansion and reproduction and thenperforming a reproducing operation due to magnetic domain expansion.Accordingly, the present embodiment is applicable to an arbitrarymagneto-optical disk apparatus which performs magnetic domain expansionand reproduction by changing the power level of laser light anddetermining as an optimal power level for magnetic domain expansion apower level of laser light that a reproduced signal coincides with apredetermined record signal.

Also, this embodiment is applicable to an arbitrary magneto-optical diskapparatus which performs magnetic domain expansion and reproduction on apredetermined record signal having been recorded on magneto-opticalrecording medium by changing the power level of laser light anddetermines as an optimal power level for magnetic domain expansion apower level of laser light that a reproduced signal coincides with thepredetermined record signal.

Accordingly, the block diagram for the magneto-optical disk apparatus isnot limited to those shown in FIG. 5 or FIG. 19. An apparatus may beusable which comprising a block diagram that can realize the aboveexplained function.

Also, the reproducing method may be a producing method that determinesan optimal power level of laser light for magnetic domain expansion andthen effecting magnetic domain expansion and reproduction using thedetermined power level of laser light.

Furthermore, the magnetic material structure for the magneto-opticalrecording medium 10 of this invention is not limited to that shown inFIG. 2, but may be one that can transfer with expanding a magneticdomain in the recording layer into the reproducing layer.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A reproducing apparatus for a magneto-opticalrecording medium to transfer, during reproduction, a magnetic domainrecorded within a recording layer into a reproducing layer, comprising:an optical means for illuminating laser light with a predeterminedintensity not to cause transfer of said magnetic domain from saidrecording layer to said reproducing layer; and a magnetic field applyingmeans for applying alternating magnetic field to said magneto-opticalrecording medium; wherein said magnetic domain is transferred withexpansion from said recording layer to said reproducing layer byapplying alternating magnetic field to said magneto-optical recordingmedium in a state that said predetermined intensity of laser light isilluminated to said magneto-optical recording medium.
 2. A reproducingapparatus according to claim 1, wherein said magnetic field applyingmeans applies alternating magnetic field in response to a timing signal.3. A reproducing apparatus according to claim 2, further comprising atiming signal generating means for generating said timing signal insynchronism with an external sync signal to be obtained based on aphysical structure of said magneto-optical recording medium.
 4. Areproducing apparatus according to claim 3, wherein said timing signalgenerating means includes an external sync signal creating circuit tocreate said external sync signal based on said physical structure.
 5. Areproducing apparatus according to claim 4, wherein said magneto-opticalrecording medium has a track of a land/groove scheme and includes adiscontinuous region formed with said groove at predetermined interval,said external sync signal creating circuit creating said external syncsignal responsive to said discontinuous region.
 6. A reproducingapparatus according to any of claims 1 to 5, wherein said optical meansincludes an intensity adjusting means to adjust an intensity of laserlight.
 7. A reproducing apparatus according to claim 6, wherein saidmagneto-optical recording medium includes a particular region previouslyrecorded with a signal to adjust an intensity of said laser light bysaid intensity adjusting means.
 8. A recording apparatus according toclaim 7, wherein said particular region is formed for each sector.
 9. Areproducing apparatus according to claim 7, wherein said particularregion is formed for each zone.
 10. A method of reproducing with amagneto-optical recording medium to transfer, during reproduction, amagnetic domain recorded within a recording layer into a reproducinglayer, comprising: (a) illuminating laser light with a predeterminedintensity not to cause transfer of said magnetic domain from saidrecording layer to said reproducing layer; and thereafter (b) applyingalternating magnetic field to said magneto-optical recording medium,whereby said magnetic domain is transferred with expansion from saidrecording layer to said roducing layer.